Synthetic and natural rubbers have a variety of unique and useful physical properties. In an uncured or natural state, such materials generally exhibit properties that are less than optimal for everyday or industrial use. Accordingly, rubber compositions are generally reacted with crosslinkers such as those containing sulfur or peroxides in order to cure the rubber. In general, heat is applied to a rubber composition during a molding operation to produce molded articles having desired physical properties.
Athletic footwear have rubber outsoles that meet a variety of performance specifications. The outsoles are generally prepared from silica filled rubber compositions by heating the compositions for suitable times and temperatures in compression molds. To compatibilize the rubber resins with the filler and improve the physical properties, silane coupling agents are commonly used.
Typical rubber compounds require the use of a process oil to facilitate both compounding and processing. As a rule, the process oils come from petroleum. As such, they represent a non-renewable resource, and can contain a variety of potentially harmful components such as aromatic compounds. The process oils may be hydrotreated to remove at least a large portion of the aromatic compounds; however such a hydrotreatment step adds increased costs.
Under some manufacturing conditions it is economically feasible to replace petroleum based components in a rubber composition with components from renewable sources. For example, it has been proposed to replace mineral oil in tires with vegetable oil at relatively high levels in order to produce tires having a greater proportion of renewable resources that have an acceptable rolling resistance. Under other conditions, it is desirable to reduce or completely eliminate the level of certain processing agents such as silanes in rubber compositions. It has been found that the use of low levels of a non-petroleum oil in rubber compositions leads to the use of a greater amount of renewable resources in the compositions, and can provide other health and technological benefits.